Optical fibers have been used in conjunction with laser systems to treat venous reflux for several years. The procedure involves placing an optical fiber in the vein and transmitting laser light through the fiber to the vein walls, causing the vein to close. In current vein ablation systems, an optical fiber is inserted into the vein, either bare or through an introducer sheath. In the latter case, the fiber tip is positioned outside and distal of the distal end of the introducer sheath during the procedure. In either case, when laser light is transmitted to the fiber, the fiber tip may become very hot, potentially causing its cladding and/or buffer material to burn inside the patient's body. In addition, if a hot fiber tip contacts the vein wall, it may cause perforations which can result in bruising and patient discomfort.